Retroreflective materials are employed for various safety and decorative purposes. Particularly, these materials are useful at nighttime when visibility is important under low light conditions. With perfect retroreflective materials, light rays are reflected essentially towards a light source in a substantially parallel path along an axis of retroreflectivity. Retroreflective materials can be used as reflective tapes and patches for clothing such as vests and belts. Also, retroreflective materials can be used on posts, barrels, traffic cone collars, highway signs, vehicles, warning reflectors, etc. Retroreflective material can include arrays of randomly oriented micron diameter spheres or close packed cube-corner (prismatic) arrays.
Cube-corner or prismatic retroreflectors are described, for example, in U.S. Pat. No. 3,712,706, issued to Stamm on Jan. 23, 1973, the teachings of which are incorporated by reference herein. Generally, the prisms can be made by forming a master negative die on a flat surface of a metal plate or other suitable material. To form the cube-corner elements, three series of parallel equidistance intersecting V-shaped grooves 60 degrees apart are inscribed in the flat plate. The die is then used to process the desired cube-corner array into a rigid flat plastic surface.
Further details concerning the structures and operation of cube-corner microprisms can be found in U.S. Pat. No. 3,684,348, issued to Rowland on Aug. 15, 1972, the teachings of which are incorporated by reference herein. A method for making retroreflective sheeting is also disclosed in U.S. Pat. No. 3,689,346 issued to Rowland on Sep. 5, 1972, the teachings of which are incorporated by reference herein. For example, cube-corner microprisms can be formed in a cooperatively configured mold. The prisms can be bonded to sheeting, which is applied thereover to provide a composite structure in which the cube-corner elements project from one surface of the sheeting.
Adhesively mounted retroreflective materials are prone to wrinkling when applied to contoured surfaces. In some instances, it has been necessary to cut a retroreflective structure to a specific geometry to prevent wrinkles when the retroreflective structure was applied to a contoured surface. In addition, many adhesively mounted retroreflective materials have been susceptible to shrinkage. The problems of wrinkling and shrinkage have heretofore hindered the application of retroreflective materials to contoured surfaces.